ITO dispersion, ITO film, multilayer object including ITO film, and method for producing ITO dispersion and ITO film

Abstract

An ITO dispersion for use in forming an ITO film by a wet process, the ITO dispersion including first ITO particles and second ITO particles, wherein the first ITO particles have a particle diameter distribution which has a first peak corresponding to a first average particle diameter and the second ITO particles have a particle diameter distribution which has a second peak corresponding to a second average particle diameter that differs from the first average particle diameter.

Description

ITO dispersion, ITO film, laminate including ITO film, and method for manufacturing ITO dispersion and ITO film

[0001] The present invention relates to an ITO (Indium Tin Oxide) dispersion, an ITO film, a laminate including an ITO film, an ITO dispersion, and a method for manufacturing an ITO film.

[0002] ITO particles can be used as a film-forming material in a wet process by adding a solvent or the like to form a solution (ink). This solution (ink) can also be used to produce a thin film by a wet process.

[0003] WO2019 / 138707

[0004] The ITO particles described in Patent Document 1 have excellent intra-particle conductivity due to the uniform crystal orientation within the particles. However, electrons generally scatter at particle interfaces, which can reduce the conductivity of ITO films containing ITO particles. Furthermore, when using a mist deposition method to manufacture ITO films, additives may be added to the solution to address the above-mentioned issues. However, adding additives to the solution can cause problems such as a failure to generate mist. Therefore, in the present invention, an ITO film is manufactured using a dispersion liquid containing a first group of ITO particles having a first particle size distribution and a second group of ITO particles having a second particle size distribution different from the first particle size. It has been found that this method improves the conductivity of the ITO film.

[0005] One aspect of the present invention is an ITO dispersion used for wet-forming an ITO film, the ITO dispersion including a first group of ITO particles and a second group of ITO particles, the first group of ITO particles having a first peak at a first particle size in a particle size distribution, and the second group of ITO particles having a second peak at a second particle size different from the first particle size in a particle size distribution. Also, the ITO dispersion used for wet-forming an ITO film includes a first group of ITO particles having a first average particle size and a second group of ITO particles having a second average particle size larger than the first average particle size, the difference between the first average particle size and the second average particle size being 10 nm or more and 30 nm or less. Also, an ITO dispersion liquid used for wet film formation of an ITO film is an ITO dispersion liquid containing a first group of ITO particles in which 90% or more of the particle size distribution has a particle size of 5 nm or more and 30 nm or less, and a second group of ITO particles in which 90% or more of the particle size distribution has a particle size of 34 nm or more and 45 nm or less.

[0006] Another aspect of the present invention is a method for producing an ITO film by forming an ITO film by a wet method using the above-described ITO dispersion liquid, or by forming an ITO film by a mist film-forming method using the above-described ITO dispersion liquid.

[0007] Another aspect of the present invention is a method for producing an ITO dispersion, which comprises mixing a first group of ITO particles, in which 90% or more of the particle size distribution has a particle size of 5 nm to 30 nm, with a second group of ITO particles, in which 90% or more of the particle size distribution has a particle size of 34 nm to 45 nm, to prepare a mixed ITO particle group, and dispersing the mixed ITO particle group in a solvent. Also, a method for producing an ITO dispersion comprises mixing a first dispersion containing the first group of ITO particles, in which 90% or more of the particle size distribution has a particle size of 5 nm to 30 nm, with a second dispersion containing the second group of ITO particles, in which 90% or more of the particle size distribution has a particle size of 34 nm to 45 nm.

[0008] Another aspect of the present invention is an ITO film comprising a first group of ITO particles having a particle diameter of 15 nm or more and 29 nm or less and a second group of ITO particles having a particle diameter of 30 nm or more and 60 nm or less, wherein the mass ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group is 8% or more and 75% or less.

[0009] Another aspect of the present invention is a laminate including the above-described ITO film.

[0010] 1 is a graph showing the particle size distribution of Example 1. 2 is a graph showing the particle size distribution of Example 2. 3 is a graph showing the particle distribution of Example 3. 4 is an SEM image of an ITO film including the second ITO particle group of this embodiment. 5 is an SEM image of an ITO film including the first ITO particle group of this embodiment. 6 is an SEM image of an ITO film including the first ITO particle group of this embodiment. 7 is an SEM image of an ITO film in which the first ITO particle group of this embodiment is mixed at a mass ratio of 8.33 wt % with respect to the total mass of the first ITO particle group and the second ITO particle group. 8 is an SEM image of an ITO film in which the first ITO particle group of this embodiment is mixed at a mass ratio of 24.99 wt % with respect to the total mass of the first ITO particle group and the second ITO particle group. 9 is an SEM image of an ITO film in which the first ITO particle group of this embodiment is mixed at a mass ratio of 49.98 wt % with respect to the total mass of the first ITO particle group and the second ITO particle group. 1 is an SEM image of an ITO film in which the first ITO particle group of this embodiment is mixed at a mass ratio of 74.98 wt % with respect to the total mass of the first ITO particle group and the second ITO particle group. FIG. 2 is a conceptual diagram showing an example of a film forming apparatus using a mist method in this embodiment. FIG. 3 is a diagram plotting resistance values ​​for each sample of Example 1. FIG. 4 is a diagram plotting resistance values ​​for each sample of Example 2. FIG. 5 is a diagram plotting resistance values ​​for each sample of Example 3.

[0011] An embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described below. The present embodiment is an example for explaining the present invention, and is not intended to limit the present invention to the following content. The present invention can be practiced with appropriate modifications within the scope of its gist.

[0012] <ITO Dispersion> The ITO dispersion (nano-dispersion) according to this embodiment is an ITO dispersion used for wet-forming an ITO film, and includes at least a first group of ITO particles and a second group of ITO particles, the first group of ITO particles having a first peak of a first particle size in the particle size distribution, and the second group of ITO particles having a second peak of a second particle size different from the first particle size in the particle size distribution.

[0013] The particle size distribution or particle size in the ITO dispersion liquid of this embodiment is a particle size distribution or particle size measured by dynamic light scattering (DLS).

[0014] In the ITO dispersion according to this embodiment, the difference between the first particle diameter and the second particle diameter is 10 nm or more and 30 nm or less. The lower limit of the difference between the first particle diameter and the second particle diameter is preferably 12 mm, more preferably 14 mm, and even more preferably 16 mm. The upper limit of the difference between the first particle diameter and the second particle diameter is preferably 28 mm, more preferably 26 mm, and even more preferably 24 mm.

[0015] The ITO dispersion according to this embodiment is an ITO dispersion used for wet deposition of an ITO film, and includes a first group of ITO particles having a first average particle size and a second group of ITO particles having a second average particle size larger than the first average particle size, and the difference between the first and second average particle sizes is 10 nm to 30 nm. The lower limit of the difference between the first and second average particle sizes is preferably 12 mm, more preferably 14 mm, and even more preferably 16 mm. The upper limit of the difference between the first and second average particle sizes is preferably 28 mm, more preferably 26 mm, and even more preferably 24 mm.

[0016] The ITO dispersion according to this embodiment is an ITO dispersion used for wet deposition of an ITO film, and includes a first group of ITO particles in which 90% or more of the particle size distribution has a particle size of 5 nm or more and 30 nm or less, and a second group of ITO particles in which 90% or more of the particle size distribution has a particle size of 34 nm or more and 45 nm or less.

[0017] It has been found that when an ITO film is produced using an ITO dispersion in which at least the above-mentioned two types of ITO particle groups are mixed at a desired mixing ratio, an ITO film having a lower conductivity can be obtained than an ITO film formed by wet deposition using a dispersion in which the first ITO particle group or the second ITO particle group is dispersed at a mass ratio of approximately 100%.

[0018] Factors that contribute to the conductivity of ITO films formed using a wet process using ITO particles include the number of particle interfaces and particle packing ratio. The number of particle interfaces affects the electron migration speed, and the particle packing ratio affects the number of conductive paths. Because the crystal orientation within ITO particles is aligned, the conductivity within the particles is high, but the resistance at particle-to-particle interfaces increases, hindering the movement of electrons. Therefore, for a conductive path of a given length, a conductive path composed solely of large ITO particles will have fewer particle interfaces than one composed solely of small ITO particles. Therefore, a conductive path composed solely of large ITO particles is thought to have a faster electron migration speed and improved conductivity than a conductive path composed solely of small ITO particles. In other words, the number of particle interfaces present in the conductive path affects the conductivity of the ITO film.

[0019] Next, we will explain the particle filling rate and the conductivity of ITO films. In theory, if the ITO particle filling rate is 100%, the entire ITO film will have conductive paths. Therefore, compared to an ITO film with a particle filling rate of 50%, for example, the number of conductive paths will be greater, and the conductivity of the ITO film is expected to be higher. However, in reality, ITO particles are in point or line contact with each other, making it difficult to increase the filling rate in an ITO film containing groups of ITO particles of the same shape or similar size. Furthermore, increasing the ITO particle filling rate increases the number of particle interfaces present in the conductive paths accordingly. Therefore, to increase the conductivity of an ITO film, it is important to balance the number of particle interfaces and the particle filling rate.

[0020] Based on the above, the present inventors have found that the conductivity of an ITO film can be improved by producing an ITO film by a wet process using an ITO dispersion containing ITO particle groups having at least two types of particle size distribution.

[0021] Figure 1 shows the particle size distribution of the first ITO particle group and the particle size distribution of the second ITO particle group in the ITO dispersion of this embodiment. The solid line in Figure 1 represents the particle size distribution of the first ITO particle group, and the dashed line represents the particle size distribution of the second ITO particle group. Figure 1 shows the results of measuring the ITO dispersion by dynamic light scattering (DLS).

[0022] The particle size distributions of the second ITO particle groups shown by the dashed lines in Figures 1A to 1C are the same, while the particle size distributions of the first ITO particle groups shown by the solid lines are different in Figures 1A to 1C. The first ITO particle group in Figure 1A is the particle size distribution of the first ITO particle group in Example 1, which will be described later. Figure 1B is the particle size distribution of the first ITO particle group in Example 2, and Figure 1C is the particle size distribution of the first ITO particle group in Example 3. In Figures 1A to 1C, the first ITO particle group is present at a ratio of approximately 50 wt% with respect to the total mass of the first particle group and the second ITO particle group. The first ITO particle group in Figure 1 all has one peak in the particle size range of 19 nm to 28 nm, and in all cases, 90% or more of the particle size distribution has a particle size of 19 nm to 28 nm, and the average particle size of the first ITO particle group is 19 nm to 28 nm. The synthesis method of the first ITO particle group will be described later, but the particle size distribution of the first ITO particle group shown in Figure 1 is one example, and the particle size of the ITO particles can be adjusted by the synthesis method. Therefore, in this embodiment, the first ITO particle group is an ITO particle group whose particle size distribution peak is in the range of 5 nm to 30 nm. Also, the first ITO particle group is an ITO particle group whose average particle size is in the range of 5 nm to 30 nm. Also, the first ITO particle group is an ITO particle group whose particle size distribution is such that 90% or more of the particle size distribution has a particle size of 5 nm to 30 nm.

[0023] Next, the second ITO particle group in Fig. 1 has one peak in the particle diameter range of 35 nm to 45 nm, and 90% or more of the particles in the particle diameter distribution have a particle diameter of 35 nm to 45 nm. In this embodiment, the second ITO particle group is an ITO particle group whose particle diameter distribution peak is in the range of 35 nm to 45 nm, or an ITO particle group whose average particle diameter is in the range of 35 nm to 45 nm, or an ITO particle group whose particle diameter distribution has a particle diameter of 35 nm to 45 nm or more. Note that the particle diameter distribution of the second ITO particle group shown in Fig. 1 is an example and is not limited to Fig. 1.

[0024] In the ITO dispersion liquid according to this embodiment, the mass ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group is 8% or more and 75% or less. The lower limit of this mass ratio difference is preferably 25%. The upper limit of this mass ratio difference is preferably 50%. Details of the mass ratio will be described later in Examples 1 to 3.

[0025] As an example of the second ITO particle group in the ITO dispersion according to this embodiment, the ITO particle group disclosed in Patent Document 1 of this specification may be used. FIG. 2A shows a scanning electron microscope photograph of an ITO film containing only the ITO particle group described in Patent Document 1 as the second ITO particle group of this embodiment. The ITO particle group (second ITO particle group) of Patent Document 1 is a particle having a plurality of curved irregularities on its surface, preferably a non-rectangular shape, with nine or more protrusions (a shape in which nine or more child particles are bonded to a seed particle). Here, "non-rectangular shape" means that the particle has seven or more faces. For example, a roughly rectangular shape with six faces, a roughly cubic shape, a three-dimensional shape with five or fewer faces, a spherical shape, etc. are not included in the "non-rectangular shape" referred to here. In other words, the non-rectangular shape of the ITO particles does not correspond to a rectangular shape (a shape with eight protrusions). A specific shape of the ITO particles according to this embodiment preferably has nine or more protrusions.

[0026] A scanning electron microscope (SEM) photograph of an ITO film containing only the first ITO particle group of this embodiment is shown in Figure 2B. As can be seen from a comparison of Figures 2A and 2B, the first ITO particle group has fewer protrusions than the second ITO particle group, which is the ITO particle group of Patent Document 1, and has more rectangular parallelepiped-shaped ITO particles than in Figure 2A. Also, Figure 2B shows smaller ITO particle sizes than Figure 2A.

[0027] The ITO particles (second ITO particle group) in Patent Document 1 have curved irregularities on their surfaces, which may lead to more gaps between particles than rectangular ITO particles. Therefore, by mixing the second ITO particle group with the smaller first ITO particle group, the particle packing rate can be increased and the conductivity of the ITO film can be improved. Furthermore, the ITO particles in Patent Document 1 (the second ITO particle group in this embodiment) have multiple curved irregularities on their surfaces, while the first ITO particle group in this embodiment has fewer protrusions and different ITO particle shapes. Mixing ITO particles of different sizes and particle shapes can increase the particle packing rate and improve the conductivity of the ITO film.

[0028] The ITO dispersion according to this embodiment may further include a third ITO particle group. The third ITO particle group may be a particle group larger than the second ITO particle group. For example, the third ITO particle group has a peak in its particle size distribution at a particle size larger than the peak particle size of the second ITO particle group. Alternatively, the third ITO particle group has an average particle size larger than the average particle size of the second ITO particle group. Alternatively, the third ITO particle group has a particle size of 100 nm or more and 160 nm or less, with 90% or more of the particle size distribution being 100 nm or more. By setting the peak particle size, average particle size, or particle size accounting for 90% or more of the particle size distribution of the third ITO particle group to 100 nm or more, an ITO film with a larger film thickness and lower resistance can be produced compared to using only the first and second ITO particle groups.

[0029] ITO particles (third particles) having a particle diameter of about 100 nm or more can be produced by a known method, for example, the method described in “Growth of Conductive Indium Tin Oxide (ITO) Nanoparticles by Mineralization in Ring-Shaped Biomimetic Templates” J. Phys. Chem. C 2009, 113, 40, 17372-17377.

[0030] In the ITO dispersion liquid according to this embodiment, the solvent is not particularly limited, but examples thereof include water, alcohols such as methanol, ethanol, and isopropyl alcohol, and mixed solvents thereof. Among these, water and alcohols are preferred, and water is more preferred. That is, the dispersion liquid according to this embodiment can be suitably used as an aqueous dispersion liquid.

[0031] When forming an ITO film on a film substrate, the film substrate is more water-repellent than glass, and hydrophilization treatments (UV or plasma irradiation) typically performed on glass are less effective at hydrophilizing the film substrate. Therefore, hydrophilization has often been achieved by applying a resin-based undercoat agent to the film substrate. However, these resin-based undercoats cannot withstand the strong acid or strong alkali used as an etching solution for the ITO film and peel off, resulting in the ITO film itself peeling off along with the resin-based undercoat agent.

[0032] Therefore, the applicant discovered that adding polysiloxane to an ITO dispersion liquid increases the affinity and adhesion to the film substrate. By including polysiloxane in the ITO dispersion liquid, it is possible to produce an ITO film (described below) that has high adhesion to the film substrate without using existing hydrophilic treatments for the film substrate. This eliminates the need for existing resin-based undercoating agents, and the ITO film will not peel off even when etched with a strong acid or strong alkali treatment.

[0033] Furthermore, as another effect, it was found that regardless of the ITO dispersion, the atomization of the dispersion by ultrasonic treatment used in the mist film formation method is promoted in the nanoparticle dispersion containing polysiloxane. This is thought to be because the polysiloxane reduces the surface tension of the nanoparticle dispersion, promoting atomization. The effect of promoting atomization by adding the polysiloxane to the dispersion can be obtained in any solution in which polysiloxane dissolves, regardless of the ITO dispersion.

[0034] The content of polysiloxane in the ITO dispersion liquid according to this embodiment is preferably 1.0% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.05% by mass or less. A preferred polysiloxane is polyether-modified dimethylsiloxane.

[0035] The ITO dispersion according to this embodiment may contain other additives as needed. When ordinary ITO particles are dispersed in a solvent for a long period of time, a surfactant is required to prevent the ITO particles from aggregating. However, the ITO dispersion according to this embodiment can be a dispersion in which ITO particles can be dispersed for a long period of time without the addition of a surfactant. Therefore, the dispersion according to this embodiment can be a dispersion that does not substantially contain a surfactant, i.e., a surfactant-free dispersion. The surfactant referred to here refers to a substance that adsorbs to the particle surface and has the function of dispersing the particles in a dispersion medium. Specific examples include anionic surfactants, cationic surfactants, and nonionic surfactants.

[0036] In the ITO dispersion liquid according to this embodiment, the ratio (volume ratio) of ITO particles to the solvent is not particularly limited, but is preferably 40% or less. By setting it in this range, the ITO particles can be stably monodispersed for a long period of time.

[0037] <ITO Film> Figure 3 shows a scanning electron microscope (SEM) image of an ITO film produced by a mist film-forming method using the ITO dispersion liquid of Example 2 described below. For comparison, Figure 2A is a scanning electron microscope image of an ITO film produced using a dispersion liquid in which only the second ITO particle group is dispersed. Figure 2B is a scanning electron microscope image of an ITO film produced using a dispersion liquid in which only the first ITO particle group is dispersed. As can be seen from the image, in Figure 2A, the size of each particle is large and there are many gaps between the particles. In contrast, in Figure 2B, the size of the particles is smaller than in Figure 2A and the gaps between the particles are smaller than in Figure 2A.

[0038] Figure 3A shows an ITO film formed by mist deposition using an ITO dispersion in which the first ITO particle group is mixed at a mass ratio of approximately 8 wt% relative to the total mass of the first ITO particle group and the second ITO particle group. Similarly, Figure 3B shows the mass ratio of the first ITO particle group at approximately 25 wt%, Figure 3C shows the mass ratio at approximately 50 wt%, and Figure 3D shows the mass ratio at approximately 75 wt%. From Figure 3A to Figure 3D, it can be seen that as the mass ratio of the second ITO particle group increases, the size of the ITO particles becomes smaller overall.

[0039] In this embodiment, the particle size distribution of the ITO dispersion was measured by dynamic light scattering (DLS). Meanwhile, the particle size of the ITO particles contained in the ITO film of this embodiment was calculated from an SEM image. Specifically, the particle size of the ITO particles was determined as the average value of the longest particle diameter (major axis) and the shortest particle diameter (minor axis) among the particle diameters passing through the center points of the ITO particles shown in the SEM image of FIG. 3 . This means that the particle size is calculated by the above method regardless of whether the ITO particles are spherical or rectangular. ITO particles with a particle diameter in the range of 15 nm to 29 nm are referred to as first ITO particles, and ITO particles with a particle diameter in the range of 30 nm to 60 nm are referred to as second ITO particles.

[0040] It has been found that an ITO film manufactured using the ITO dispersion of this embodiment is manufactured by mixing a first ITO particle group and a second ITO particle group in a mass ratio similar to that of the at least two particle groups contained in the ITO dispersion.

[0041] A method for calculating the mass ratio of the particle groups from a scanning electron microscope photograph of the manufactured ITO film will be described below. As described above, the particle diameters (r) of the first ITO particles and the second ITO particles are determined from the scanning electron microscope photograph of the ITO film, and the volumes (4 / 3πr ３ ) is obtained. The mass of the first ITO particle group and the second ITO particle group can be calculated by multiplying the obtained volume by the specific gravity of the ITO particles. In this way, the mass ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group is calculated from the produced ITO film.

[0042] The ITO film according to this embodiment includes a first group of ITO particles having a particle diameter of 15 nm or more and 29 nm or less, and a second group of ITO particles having a particle diameter of 30 nm or more and 60 nm or less.

[0043] The lower limit of the particle diameter of the first ITO particle group in the ITO film according to this embodiment is preferably 16 nm, more preferably 18 nm, and even more preferably 21 nm, and the upper limit of the particle diameter of the first ITO particle group is preferably 28 nm, more preferably 26 nm, and even more preferably 23 nm.

[0044] The lower limit of the particle diameter of the second ITO particle group in the ITO film according to this embodiment is preferably 32 nm, more preferably 35 nm, and even more preferably 40 nm, and the upper limit of the average particle diameter of the second ITO particle group is preferably 58 nm, more preferably 55 nm, and even more preferably 50 nm.

[0045] In the ITO film according to this embodiment, the mass ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group is 8% or more and 75% or less. The lower limit of this mass ratio is preferably 25%. The upper limit of this mass ratio is preferably 50%.

[0046] The ITO film according to this embodiment may further include a third ITO particle group. The third ITO particle group is a particle group larger than the second ITO particle group. For example, the third ITO particle group has a particle diameter of 100 nm or more and 160 nm or less. The third ITO particle group has an average particle diameter larger than the average particle diameter of the second ITO particle group. By including the third ITO particle group in the ITO film, an ITO film having a larger film thickness and lower resistance can be manufactured compared to using only the first and second ITO particle groups. Note that the particle diameter in an ITO film including the third ITO particle group is calculated in the same manner as the particle diameters of the first and second ITO particles in an SEM image.

[0047] The ITO film of this embodiment can be produced by a wet method using the ITO dispersion liquid. Examples of wet methods include spin coating, inkjet, slit coating, spraying, and dip coating. Alternatively, a mist film-forming method can be used as the wet method. Specifically, the method for producing an ITO film by the mist film-forming method preferably includes a mist-forming step of producing the ITO dispersion liquid of this embodiment into a mist, a contacting step of adhering the mist to the film-forming surface, and a drying step of drying the solvent of the mist that has adhered to the film-forming surface after the contacting step.

[0048] ITO film is a material with high conductivity and transparency, and is widely used as a transparent conductive material. Methods for manufacturing ITO films include sputtering and laser deposition, but these techniques make it difficult to form a uniform thin film on a flexible substrate, and the performance of ITO, which has excellent surface properties, is not fully utilized. Furthermore, the deposition process requires large-scale vacuum equipment, and there is room for improvement in this regard as well.

[0049] In this regard, the ITO dispersion according to this embodiment has high dispersibility without sedimentation of components, and therefore, a simple wet method can be used when forming an ITO film on a substrate. Furthermore, restrictions on the substrate material can be relaxed, and a film can be formed on the flexible substrate described above. Furthermore, according to this embodiment, even when nano-level ITO particles (ITO nanoparticles) are formed, high crystallinity and monodispersity can be stably maintained, and therefore, surface properties such as conductivity and transparency of the thin film can be controlled at a high level.

[0050] The mist-forming step in the mist film-forming method, which is one of the wet methods, can be any method that turns a dispersion into a mist (mist). Any known method can be used to generate the mist, such as a pressurized method, a rotating disk method, an ultrasonic method, an electrostatic method, an orifice vibration method, or a steam method. For the ITO dispersion of this embodiment, a physical method of turning the dispersion into a mist, such as an ultrasonic method, is suitable. This facilitates temperature control and mist size control of the ITO dispersion. Furthermore, treating the dispersion as a mist provides high controllability and eliminates problems such as distortion during thin film formation, which are common in methods such as sol-gel methods that require liquid supply.

[0051] In the mist-forming step, a carrier gas is used to transport the mist to the deposition surface in the subsequent contact step. Examples of the carrier gas that can be used include inert gases such as argon, helium, and nitrogen. Between the mist-forming step and the contact step, a step of homogenizing the mist using a mist trap or a retention step of providing a retention period (retention area) for the mist may be performed.

[0052] The contacting step is not particularly limited as long as it is a method of contacting the mist with the surface to be formed, and known techniques can be used. For example, a method of spraying the fine droplets obtained in the mist-forming step onto the substrate by a mist method can be used. Examples of the mist method include ultrasonic spraying, mist CVD, a Sonia source method, and a hot wall method. These methods can be selected taking into consideration the film thickness of the ITO film to be formed on the substrate, the size of the droplets to be sprayed, and the like.

[0053] The contacting step may be carried out under atmospheric pressure, reduced pressure, or vacuum, but atmospheric pressure is preferred for simplicity. Furthermore, applying the mist dispersion onto a masked substrate enables the formation of fine patterns. This is particularly suitable for forming a thin film of ITO nanoparticles on a substrate surface. This allows for highly accurate dimensional control.

[0054] When water is used as the solvent for the dispersion, it is preferable to use a water-repellent masking material (water-repellent film) as the masking material for the surface on which the film is to be formed. This enables pattern formation with even higher precision. Furthermore, since the material constraints on the substrate, which is the surface on which the film is to be formed, are relaxed, a thin and highly flexible film substrate (sometimes called a sheet substrate) can also be used as the substrate. Furthermore, continuous production such as roll-to-roll is also possible.

[0055] The substrate may be made of a known material, such as glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyetherimide, polyetheretherketone, polyphenylene sulfide, polyarylate, polyimide, polycarbonate (PC), cellulose triacetate (TAC), or cellulose acetate propionate (CAP).

[0056] The drying process involves removing the solvent from the mist adhering to the surface on which the film is to be formed. For example, the solvent is vaporized by irradiation with infrared light or other light, heating, or the like, thereby forming an ITO film on the surface of the surface on which the film is to be formed. The heating temperature can be set taking into consideration the boiling point of the solvent, the softening point of the substrate, and other effects on the physical properties of the ITO film. The softening point of the substrate here refers to the temperature at which the substrate softens and begins to deform when heated, and can be determined, for example, by a test method in accordance with JIS K7191-1.

[0057] It is preferable to include a step of immersing the ITO film in a weak acid after the drying step. Immersing the ITO film in a weak acid can further increase the conductivity of the ITO film. The weak acid is preferably an acid with a pH of 3 to 4 or less, and oxalic acid is particularly preferable. Since ITO particles grow from a central nucleus, it is thought that the outer periphery of the particle contains more amorphous components. Therefore, the resistance value of the ITO particles is higher in the outer periphery than in the interior. Therefore, by immersing the ITO film in a weak acid and removing the amorphous components in the outer periphery of the ITO particles, the conductivity of the ITO film can be improved.

[0058] After the drying step, if necessary, a step of slowly cooling the substrate on which the ITO film has been formed (slow cooling step) or a UV irradiation step for the purpose of modifying the base material, such as imparting hydrophilicity, may be carried out.

[0059] 4 is a conceptual diagram showing an example of a film formation apparatus using the mist film formation method of this embodiment. The film formation apparatus 1 has a first tank that generates mist containing ITO particles, a second tank that is a mist trap that homogenizes the mist, and a third tank that sprays the mist onto a substrate 10.

[0060] The first tank contains the above-described ITO dispersion liquid as a raw material solution S. The particles in the dispersion liquid may be any of those described above, but nanoparticles are preferred. In this example, ITO particles are used as the particles.

[0061] Air 20 is flowed through the first tank to form a mist flow path. An ultrasonic vibrator 30 is housed in the first tank. The ultrasonic vibrator 30 turns a dispersion liquid containing ITO particles into mist. The mist-forming process is carried out in the first tank. The mist generated in the first tank is transported to the second tank via a pipe provided in the first tank. In the second tank, excess mist accumulates at the bottom of the tank, and mist with a more uniform particle size is transported to the third tank via a pipe provided in the second tank.

[0062] A substrate 10 is placed in the third tank, and the mist transported from the second tank is sprayed onto the substrate. The mist is sprayed onto the substrate 10 in the third tank for a predetermined time. The dispersion medium of the mist adhering to the substrate 10 then evaporates, forming an ITO film on the surface of the substrate 10. A contacting step and a drying step are performed in the third tank. Note that if a certain amount of time has passed since spraying, new mist will adhere to the substrate 10 before the mist evaporates, causing the droplets of the dispersion liquid to flow down, preventing the formation of a uniform ITO film on the substrate 10. The time to stop spraying the mist onto the substrate 10 may be the time when the mist containing ITO particles liquefies and flows down from the substrate 10, or the time when an ITO film of the desired thickness has been formed on the substrate 10.

[0063] If the substrate 10 is excessively heated in the third tank, it may be deformed due to softening. Therefore, it is preferable that the mist is sprayed in the third tank at a temperature lower than the softening point of the substrate to form the ITO film. Furthermore, if the substrate 10 is heated to a temperature higher than a predetermined temperature while the mist is being sprayed, the ITO particles attached to the substrate 10 will aggregate. As a result, the uniformity of the film will deteriorate and the conductive network between the particles will be hindered, resulting in the formation of an ITO film with a high resistance value. For this reason, it is more preferable that the mist be sprayed at a temperature of 40°C or lower (e.g., 10 to 40°C) to form the ITO film.

[0064] When selectively forming a metal oxide film on the substrate 10, a water-repellent film is selectively formed on the substrate 10 in advance, and the mist is then deposited on the hydrophilic portions. If the substrate 10 is placed horizontally, the dispersion liquid deposited on the water-repellent portions will not be water-repellent, and the metal oxide film cannot be selectively formed. For this reason, in the third tank, it is preferable to spray the mist onto the substrate 10 that is tilted relative to the horizontal plane.

[0065] Similarly, in the third tank, it is preferable that the mist be sprayed onto the substrate 10 that is tilted with respect to a plane perpendicular to the direction of mist spraying, in order to remove excess ITO particles adhering to the water-repellent portion with the force of the mist spray.

[0066] In addition to the above-mentioned ultrasonic vibrator 30, other methods of generating mist include an electrostatic method in which mist is generated by applying a voltage directly to a capillary tube that sprays droplets; a pressure method in which pressure is applied to increase the flow rate of gas and the resulting mist is dispersed by colliding it with the liquid; a rotating disk method in which droplets are dropped onto a rapidly rotating disk and the resulting mist is dispersed by centrifugal force; and an orifice vibration method in which droplets are passed through an orifice plate with micro-sized holes and then cut by applying vibrations using a piezoelectric element or the like to generate micro-sized droplets. These methods can be selected as appropriate depending on cost, performance, and the like. Naturally, multiple methods may be combined to generate mist.

[0067] The ITO film according to this embodiment can be used in a laminated body for a solar cell, an EL (Electroluminescence) device, or the like.

[0068] <Method for Producing ITO Particles> Method for Producing First ITO Particles The first ITO particles according to this embodiment are preferably produced by a method including the steps of: (1) reacting a 0.36 to 1.0 mol / L In salt, a 0.036 to 0.10 mol / L Sn salt, a basic compound, and a solvent at 190 to 280°C for 15 to 120 hours to obtain first ITO particle groups; and (2) washing the first ITO particle groups. The concentration of the In salt in the solution is preferably 9 to 11 times, and more preferably 10 times, the concentration of the Sn salt on a molar basis.

[0069] The lower limit of the reaction temperature in the reaction step for obtaining the first ITO particle group is preferably 180°C, more preferably 190°C, and even more preferably 220°C. The upper limit of the reaction temperature is preferably 280°C, more preferably 260°C, and even more preferably 250°C. The lower limit of the reaction time is preferably 16 hours, more preferably 48 hours, and even more preferably 72 hours. The upper limit of the reaction temperature is preferably 120 hours, more preferably 96 hours, and even more preferably 84 hours.

[0070] It is preferable to carry out a centrifugation step between the reaction step and the washing step, and the centrifugation step is preferably carried out at a rotation speed of 8,000 to 50,000 rpm for a time period of 30 seconds to 30 minutes.

[0071] 2. Method for Producing Second ITO Particles Preferably, the method for producing ITO particles comprises: (1) a reaction step of reacting in a solution containing 0.09 to 0.9 mol / L of an In salt, 0.01 to 0.2 mol / L of an Sn salt, a basic compound, and a solvent at 190 to 200° C. for 12 to 120 hours to obtain ITO particles; and (2) a step of washing the second ITO particles.

[0072] The concentration of the In salt in the reaction solution is preferably 0.09 to 0.9 mol / L, more preferably 0.09 to 0.45 mol / L, and the concentration of the Sn salt in the reaction solution is preferably 0.01 to 0.2 mol / L, more preferably 0.01 to 0.05 mol / L.

[0073] The concentration of the In salt is preferably 4.5 to 9 times, and more preferably 5 to 9 times, the molar concentration of the Sn salt. By carrying out the particle synthesis reaction at such metal source concentrations, the ITO particles according to this embodiment can be synthesized more easily in one pot.

[0074] In the reaction step, other additives may be added as necessary to the extent that the effects of this embodiment are not impaired. The reaction time in the reaction step is preferably 12 to 120 hours, more preferably 24 to 72 hours. The reaction temperature in the reaction step is preferably 190 to 200°C.

[0075] To produce the ITO particles according to this embodiment, it is preferable to increase the concentration of the metal source and to use a relatively low base concentration relative to the metal source, which allows for further heterogeneous nucleation to proceed on the generated nuclei rather than allowing particle growth after the initial nucleation reaction, thereby synthesizing the ITO particles according to this embodiment.

[0076] In this embodiment, a centrifugation step is preferably carried out between the reaction step and the washing step. The centrifugation step is preferably carried out at a rotation speed of 8,000 to 50,000 rpm for a time period of 5 to 15 minutes.

[0077] Common features of the manufacturing methods of the first ITO particles and the second ITO particles The In salt is not particularly limited, and any known ITO raw material can be used. For example, InCl ３ metal salts such as In ２ (C ２ O ４ ) ３ , In(NO ３ ) ３ , In ２ (SO ４ ) ３ and hydrates thereof. Among these, anhydrous salts and metal salts are preferred, metal salts are more preferred, and InCl ３ is more preferred.

[0078] The Sn salt is not particularly limited, and any known Sn salt as a raw material for ITO can be used. For example, SnCl ２ , SnCl ４ , Sn ２ (C ２ O ４ ) ３ , Sn(NO ３ ) ２ , SnSO ４ , InCl ３ metal salts such as In ２ (C ２ O ４ ) ３ , In(NO ３ ) ３ , In ２ (SO ４ ) ３ and hydrates thereof. Among these, anhydrous salts and metal salts are preferred, metal salts are more preferred, and SnCl ２ , SnCl ４ is more preferred.

[0079] The basic compound is not particularly limited as long as it can neutralize the reaction solution and precipitate an In—Sn hydroxide (neutralization coprecipitation). Known basic compounds can be used. Examples include tetramethylammonium hydroxide (TMAH) and sodium hydroxide.

[0080] The concentration of the basic compound in the reaction solution is not particularly limited, but from the viewpoint of particle synthesis, it is preferably 1 to 2 mol / L, and more preferably 1.5 to 1.7 mol / L.

[0081] The solvent may be any solvent capable of dissolving the In salt, Sn salt, basic compound, and other additives used as needed. Known solvents may be used, and preferred examples include water and alcohols such as methanol, ethanol, and isopropanol.

[0082] The reaction process may be carried out in an open system, but an autoclave is preferable. This can promote the formation of an indium hydroxide-tin hydroxide coprecipitate in the reaction system. The mechanism by which the ITO particles according to this embodiment are obtained by the above-described production method is unclear, but it is believed that factors such as controlling the metal salt concentration (mol / L) in the reaction system, the reaction temperature, and the reaction time may have an effect. While the shape of monodispersed particles can be controlled by the number of nuclei generated in the system and the amount of material present therein, it is believed necessary to maintain the nuclei in the gel network and allow further heterogeneous nucleation to occur. Therefore, it is believed that it is best to increase the concentration of the metal source and use a small amount of base relative to the metal source. This allows the concentration of the metal oxide precursor capable of nucleation to be maintained for a long period of time. It is believed that the ITO particles according to this embodiment can be synthesized by combining the above-described conditions. (However, the effects of this embodiment are not limited to these.)

[0083] In the step of washing the ITO particles, washing is preferably carried out using water, alcohols such as ethanol, etc. When washing with water, it is preferable to use distilled water or pure water such as ion-exchanged water (IEW). It is also preferable to wash the dispersion by treating it with an ultrasonic cleaner.

[0084] Conventionally, a freeze-drying step and a reduction baking step are performed after the reaction step, but in this embodiment, these steps do not have to be performed. From this perspective, it is preferable not to perform a baking step, especially after the cleaning step. This prevents the ITO particles from agglomerating and maintains a monodispersed state in the dispersion medium.

[0085] <Method for Producing ITO Dispersion> There are several methods for producing the ITO dispersion according to this embodiment, and for example, the following method is used: An ITO dispersion is produced using ITO particles produced by the above-described method for producing ITO particles.

[0086] In one example, a first group of ITO particles in which 90% or more of the particle size distribution has a particle size of 5 nm or more and 30 nm or less is mixed with a second group of ITO particles in which 90% or more of the particle size distribution has a particle size of 34 nm or more and 45 nm or less to prepare a mixed group of ITO particles, and the mixed group of ITO particles is dispersed in a solvent to produce an ITO dispersion liquid.

[0087] In another example, an ITO dispersion is produced by mixing a first dispersion containing a first group of ITO particles in which 90% or more of the particle size distribution has a particle size of 5 nm or more and 30 nm or less, and a second dispersion containing a second group of ITO particles in which 90% or more of the particle size distribution has a particle size of 34 nm or more and 45 nm or less.

[0088] Furthermore, the proportion of ITO particles having a size of 5 nm or more and 30 nm or less in the particle distribution of the first ITO particle group is preferably 95% or more.

[0089] The proportion of ITO particles having a size of 34 nm or more and 45 nm or less in the particle distribution of the second ITO particle group is preferably 95% or more.

[0090] The solvent used in the method for producing an ITO dispersion according to this embodiment is the same as the solvent for the ITO dispersion described above.

[0091] The ITO dispersion and ITO film will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0092] <Measurement of ITO Particles> Scanning electron microscope photographs (SEM images) were observed using a JSM-7900F manufactured by JEOL Ltd. DLS measurements were carried out using a nanoPartica SZ-100 manufactured by Horiba Ltd.

[0093] Example 1: Tetramethylammonium hydroxide (TMAH) was dissolved in a 2-propanol solvent to a concentration of 1.6 mol / L as a basic catalyst to prepare a 2-propanol solution containing TMAH. Next, a methanol solution with an In concentration of 0.36 mol / L and an Sn concentration of 0.04 mol / L was prepared. This was added to the TMAH 2-propanol solution, stirred for 10 minutes, and then heated at 200°C for 16 hours to allow the reaction to proceed. The mixture was then centrifuged at 14,000 rpm for 10 minutes. The mixture was then washed twice with ethanol and twice with ion-exchanged water to obtain a dispersion containing a first group of ITO particles.

[0094] A reaction vessel was charged with 7.5 mL of methanol as a solvent and 1.6 mol / L of tetramethylammonium hydroxide (TMAH) as a basic catalyst. A methanol solution was then prepared so that the In concentration in the reaction solution was 0.36 mol / L and the Sn concentration was 0.04 mol / L (In / Sn = 9 in the reaction solution). This was added to the TMAH methanol solution, stirred for 10 minutes, and then heated at 190 ° C for 1 day to allow the reaction to proceed. Then, the mixture was centrifuged at 14,000 rpm for 10 minutes. The mixture was then washed twice with ethanol and twice with ion-exchanged water to obtain a dispersion containing a second ITO particle group.

[0095] A dispersion containing the first ITO particles was added to a dispersion containing the second ITO particle group to prepare a dispersion containing two types of particles. Mist film formation was performed using this dispersion as a raw material to obtain an ITO thin film. The mass ratio was calculated from the concentration ratio of the two liquids mixed together, and was used as the mass ratio of the respective ITO particles.

[0096] ITO thin film is Ar-H ２The resulting ITO transparent conductive film was baked at 150°C for 60 minutes in a reflux atmosphere of 4% CO₂ to obtain a transparent conductive ITO film. An EL device was fabricated by depositing an EL layer, including a light-emitting layer, between the pair of electrodes, with a total thickness of 150 nm, using the ITO transparent conductive film as the lower electrode and Al as the upper electrode. The low resistance of the ITO film shown in Figure 5 is achieved by mixing two types of ITO particles with different particle size ranges, thereby improving the ITO particle packing density and balancing the number of particle interfaces. The arrows in Figure 5 indicate the area where the fabricated EL device emitted light. The EL device emitted light when the surface roughness of the lower electrode, an ITO film, was minimal and the EL layer was not discontinuous due to the ITO film roughness.

[0097] The measurement results for each sample in Example 1 are shown in Table 1 and Figure 5. As shown in Table 1 and Figure 5, when the ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group, based on mass %, was in the range of 8.33 to 49.98, it was found that the resistance value of the ITO film was lower than that of Sample No. 1-1, which contains 100% second ITO particles. It was also found that the resistance value of the ITO film was lower than that of Sample No. 1-13, which contains approximately 100 wt% first ITO particles. Furthermore, light emission from the EL element was confirmed when the ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group, based on mass %, was in the range of 24.99 to 66.64.

[0098] On the other hand, when the first ITO particles are 58.31 wt % or more, the sheet resistance of the ITO film increases, and the resistance becomes high. This is presumably because the number of particle interfaces in the film increases rather than the effect of improving the filling rate of the ITO particles, resulting in the high resistance of the ITO film.

[0099] The second ITO particles have a particle diameter of 30 to 60 nm, and the thickness of the EL layer between the anode and cathode is approximately 150 nm. Therefore, if two or three or more second ITO particles overlap, the unevenness of the ITO film will break through the EL layer, causing the EL layer to not emit light. The following reasons are thought to explain why the EL layer emits light when the first ITO particles, which have a smaller particle diameter, are mixed with the second ITO particles. One is that the large steps of the second ITO particles are alleviated by the first ITO particles, which have a smaller particle diameter, preventing the EL layer from breaking apart. The other is that the presence of the first ITO particles reduces the probability of multiple second ITO particles overlapping in the film thickness direction of the EL layer.

[0100] Therefore, when the ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group on a mass % basis was in the range of 24.99 to 49.98, an EL element capable of emitting light could be obtained using a low-resistance ITO film. In other words, by using the EL element produced in this Example 1, a power-saving EL element and EL panel could be obtained.

[0101]

[0102] Example 2: Tetramethylammonium hydroxide (TMAH) was dissolved in an ethylene glycol solvent to a concentration of 2.0 mol / L as a basic catalyst to prepare an ethylene glycol solution containing TMAH. A methanol solution with an In concentration of 1.0 mol / L and an Sn concentration of 0.1 mol / L was then prepared. This was added to the ethylene glycol solution containing TMAH, stirred for 10 minutes, and then heated at 220°C for 96 hours to allow the reaction to proceed. The mixture was then centrifuged at 14,000 rpm for 10 minutes. The mixture was then washed twice with ethanol, twice with ion-exchanged water, and finally centrifuged at 4,000 rpm for 20 minutes to remove coarse particles, thereby obtaining a dispersion containing a first ITO particle group.

[0103] To this dispersion containing the first ITO particles, the dispersion containing the second ITO particles prepared by the method described in Example 1 was added to prepare a dispersion containing two types of particles. Mist film formation was performed using this dispersion as a raw material to obtain an ITO thin film. The mass ratio was calculated using the same method as in Example 1.

[0104] ITO thin film is Ar-H ２ The ITO transparent conductive film was baked at 150°C for 60 minutes in a reflux atmosphere of 4% CO₂ to obtain an ITO transparent conductive film. The ITO transparent conductive film was used as the lower electrode and Al as the upper electrode, and an EL layer including a light-emitting layer was formed between the pair of electrodes to a total thickness of 150 nm to produce an EL device. The low resistance of the ITO film shown in Figure 6 is due to the same reason as in Figure 5. The arrow in Figure 6 indicates the area where the fabricated EL device emitted light.

[0105] The measurement results for each sample in Example 2 are shown in Table 2 and FIG. 6. As shown in Table 2 and FIG. 6, when the ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group, based on mass %, was in the range of 8.33 to 49.98, it was found that the resistance value of the ITO film was lower than that of Sample No. 2-1, which contains 100% second ITO particles. It was also found that the resistance value of the ITO film was lower than that of Sample No. 2-13, which contains approximately 100 wt% first ITO particles. Furthermore, light emission from the EL element was confirmed when the ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group, based on mass %, was in the range of 24.99 to 49.98.

[0106] 6, when the first ITO particles are 58.31 wt % or more, the sheet resistance of the ITO film increases, and the resistance becomes high. The consideration regarding the increase in the resistance of the ITO film is the same as in Example 1.

[0107] Therefore, when the ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group on a mass % basis was in the range of 24.99 to 49.98, an EL element capable of emitting light could be obtained using a low-resistance ITO film. In other words, by using the EL element produced in Example 2, a power-saving EL element and EL panel could be obtained.

[0108]

[0109] Example 3: Tetramethylammonium hydroxide (TMAH) was dissolved in an ethylene glycol solvent as a basic catalyst to prepare an ethylene glycol solution containing 1.6 mol / L of TMAH. Next, a methanol solution with an In concentration of 1.0 mol / L and an Sn concentration of 0.1 mol / L was prepared. This was added to the ethylene glycol solution containing TMAH, stirred for 10 minutes, and then heated at 220°C for 96 hours to allow the reaction to proceed. The mixture was then centrifuged at 14,000 rpm for 10 minutes. The mixture was then washed twice with ethanol, twice with ion-exchanged water, and finally centrifuged at 4,000 rpm for 30 seconds to remove coarse particles, thereby obtaining a dispersion containing a first ITO particle group.

[0110] To this dispersion containing the first ITO particles, the dispersion containing the second ITO particles prepared by the method described in Example 1 was added to prepare a dispersion containing two types of particles. Mist film formation was performed using this dispersion as a raw material to obtain an ITO thin film. The mass ratio was calculated using the same method as in Example 1.

[0111] ITO thin film is Ar-H ２ The ITO transparent conductive film was baked at 150°C for 60 minutes in a reflux atmosphere of 0.1% NaOH (4%) to obtain an ITO transparent conductive film. The ITO transparent conductive film was used as the lower electrode and Al as the upper electrode, and an EL layer including a light-emitting layer was formed between the pair of electrodes to a total thickness of 150 nm to produce an EL device. The low resistance of the ITO film shown in Figure 7 is due to the same reason as in Figure 5. The area where the fabricated EL device emitted light is indicated by an arrow in Figure 7.

[0112] The measurement results for each sample in Example 3 are shown in Table 3 and Figure 7. As shown in Table 3 and Figure 7, when the ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group, based on mass %, was in the range of 8.33 to 74.97, it was found that the resistance value of the ITO film was lower than that of Sample No. 3-1, which contains 100% second ITO particles. It was also found that the resistance value of the ITO film was lower than that of Sample No. 3-13, which contains approximately 100 wt% first ITO particles. Furthermore, light emission from the EL element was confirmed when the ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group, based on mass %, was in the range of 24.99 to 74.97.

[0113] 7, when the first ITO particle group is 91.63 wt % or more, the sheet resistance of the ITO film increases, and the resistance becomes high. The consideration regarding the increase in the resistance of the ITO film is the same as in Example 1.

[0114] Therefore, when the ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group on a mass % basis was in the range of 24.99 to 74.97, an EL element capable of emitting light could be obtained using a low-resistance ITO film. In other words, by using the EL element produced in Example 3, a power-saving EL element and EL panel could be obtained.

[0115]

[0116] From the above, it was found that the conductivity of the ITO film was improved by forming an ITO film by mixing the first ITO particle group with the second ITO particle group within a predetermined range. In Examples 1 and 2, the resistance of the ITO film was confirmed when the mass% of the first ITO particle group relative to the total mass of the first ITO particle group and the second ITO particle group was approximately 8 to 50. In Example 3, the resistance of the ITO film was confirmed when the mass% of the first ITO particle group relative to the total mass of the first ITO particle group and the second ITO particle group was approximately 8 to 75. Furthermore, in Examples 1 and 2, the resistance of the ITO film was confirmed to be reduced and the EL element emitted light when the mass% of the first ITO particle group relative to the total mass of the first ITO particle group and the second ITO particle group was approximately 25 to 50. In Example 3, when the mass % of the first ITO particle group relative to the total mass of the first ITO particle group and the second ITO particle group was approximately 25 to 75, the resistance of the ITO film was reduced and the EL element emitted light.

[0117] Example 4 An ITO film was obtained by mist film formation in the same manner as in Example 1. The ITO film was immersed in oxalic acid, and then the ITO film was immersed in Ar—H ２ The ITO film was then baked at 150°C for 60 minutes in a reflux atmosphere of 0.1% oxalic acid (4%) to obtain a transparent conductive film. The film thickness and electrical conductivity of the obtained ITO film were measured to determine the resistivity. The resistivity of the sample that was not immersed in oxalic acid was 1.2 x 10 -２The resistivity of the immersed sample was 1.0 × 10 -２ The resistivity decreased to Ω·cm.

[0118] Example 5: Dispersions were prepared by adding polyether-modified dimethylpolysiloxane to ITO particle dispersions at concentrations of 1.0 wt%, 0.1 wt%, and 0.05 wt%. Using these dispersions, ITO films were formed on polyethylene terephthalate (PET) substrates by a mist film-forming method. The film-forming rate for the dispersion containing 1.0 wt% polyether-modified dimethylpolysiloxane was 350 nm / min, the film-forming rate for the dispersion containing 0.1 wt% polyether-modified dimethylpolysiloxane was 300 nm / min, and the film-forming rate for the dispersion containing 0.05 wt% polyether-modified dimethylpolysiloxane was 250 nm / min. On the other hand, when an ITO film was formed using a dispersion without the addition of polyether-modified dimethylpolysiloxane, the film-forming rate was 20 nm / min.

[0119] The obtained ITO film was ２ The ITO dispersion was baked at 150°C for 60 minutes in a reflux atmosphere of 4% dimethylpolysiloxane to obtain a transparent conductive film. When an ITO dispersion without polyether-modified dimethylpolysiloxane was used, a film could not be formed directly on the PET substrate due to the high water repellency of the PET substrate. ２ After applying the nanoparticles, an ITO film was formed. From the above results, it was found that the addition of polyether-modified dimethylpolysiloxane enabled the direct formation of an ITO film on the PET substrate without the need for a hydrophilic treatment. Therefore, it was found that the hydrophilic treatment of the PET substrate, which was previously required, could be omitted.

[0120] Furthermore, the addition of polyether-modified dimethylpolysiloxane to the ITO dispersion liquid increased the film formation rate compared to when no polyether-modified dimethylpolysiloxane was added. Furthermore, the film formation rate could be further improved by increasing the concentration of polyether-modified dimethylpolysiloxane added to the ITO dispersion liquid.

[0121] The film thickness and electrical conductivity of the ITO film obtained in this example were measured to determine the specific resistance. The specific resistances of the films obtained using ITO dispersions containing 1.0 wt %, 0.1 wt %, and 0.05 wt % polyether-modified dimethylpolysiloxane were 5.0×10 -２ Ω・cm, 3.0×10 -２ Ω・cm, 1.5×10 -２ On the other hand, the resistivity of the ITO film formed using the dispersion liquid to which no additives were added was 1.5×10 -２ The resistivity of the ITO film was Ω·cm. The addition of polyether-modified dimethylpolysiloxane had no particular effect on the resistivity of the ITO film, and ITO films with the same order of resistivity were obtained regardless of whether the polyether-modified dimethylpolysiloxane was added or not.

[0122] 1... film forming apparatus, 10... substrate, 20... air, 30... ultrasonic vibrator, S... raw material solution

Claims

1. An ITO dispersion liquid used for wet deposition of an ITO film, comprising a first group of ITO particles and a second group of ITO particles, wherein the first group of ITO particles has a first peak of a first particle size in a particle size distribution, and the second group of ITO particles has a second peak of a second particle size different from the first particle size in the particle size distribution.

2. An ITO dispersion liquid used for wet deposition of an ITO film, the ITO dispersion liquid comprising a first group of ITO particles having a first average particle size and a second group of ITO particles having a second average particle size larger than the first average particle size, wherein the difference between the first average particle size and the second average particle size is 10 nm or more and 30 nm or less.

3. An ITO dispersion liquid used for wet deposition of an ITO film, the ITO dispersion liquid comprising a first group of ITO particles in which 90% or more of the particle size distribution has a particle size of 5 nm or more and 30 nm or less, and a second group of ITO particles in which 90% or more of the particle size distribution has a particle size of 34 nm or more and 45 nm or less.

4. The ITO dispersion liquid according to claim 1, wherein the difference between the first particle size and the second particle size is 10 nm or more and 30 nm or less.

5. An ITO dispersion liquid according to any one of claims 1 to 4, wherein the mass ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group is 8% or more and 75% or less.

6. The ITO dispersion liquid according to any one of claims 1 to 5, wherein the mass ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group is 25% or more and 75% or less.

7. The ITO dispersion liquid according to any one of claims 1 to 5, wherein the mass ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group is 8% or more and 50% or less.

8. The ITO dispersion liquid according to any one of claims 1 to 7, wherein the mass ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group is 25% or more and 50% or less.

9. The ITO dispersion liquid according to any one of claims 1 to 8, wherein the second group of ITO particles are particles having a plurality of curved irregularities on their surfaces.

10. The ITO dispersion liquid according to any one of claims 1 to 9, wherein the second ITO particle group is non-rectangular and has nine or more protrusions.

11. The ITO dispersion liquid according to any one of claims 1 to 10, wherein the first group of ITO particles has a smaller number of convex portions than the second group of ITO particles.

12. The ITO dispersion according to any one of claims 1 to 11, wherein the solvent of the ITO dispersion is water.

13. The ITO dispersion according to any one of claims 1 to 12, which contains a polysiloxane.

14. The ITO dispersion of claim 13, wherein the polysiloxane is a polyether-modified dimethylsiloxane.

15. The ITO dispersion according to any one of claims 1 to 14, which contains a third group of ITO particles.

16. A method for producing an ITO film, comprising forming an ITO film by a wet method using the ITO dispersion liquid according to any one of claims 1 to 15.

17. The method for producing an ITO film according to claim 16, wherein the wet method is a mist film-forming method.

18. The method for producing an ITO film according to claim 16 or 17, further comprising the step of immersing the ITO film in a weak acid after forming the ITO film.

19. The method for producing an ITO film according to claim 18, wherein the weak acid is oxalic acid.

20. A method for producing an ITO dispersion liquid, comprising mixing a first group of ITO particles, in which 90% or more of the particle size distribution has a particle size of 5 nm or more and 30 nm or less, with a second group of ITO particles, in which 90% or more of the particle size distribution has a particle size of 34 nm or more and 45 nm or less, to prepare a mixed group of ITO particles, and dispersing the mixed group of ITO particles in a solvent.

21. A method for producing an ITO dispersion liquid, comprising mixing a first dispersion liquid containing a first group of ITO particles in which 90% or more of the particle size distribution has a particle size of 5 nm or more and 30 nm or less, and a second dispersion liquid containing a second group of ITO particles in which 90% or more of the particle size distribution has a particle size of 34 nm or more and 45 nm or less.

22. A method for producing an ITO dispersion liquid according to claim 20 or 21, comprising a step of reacting a solution containing 0.36 to 1.0 mol / L of an In salt, 0.036 to 0.1 mol / L of an Sn salt, a basic compound, and a solvent at 190 to 280°C for 15 to 120 hours to produce the first ITO particle group.

23. An ITO film comprising a first group of ITO particles having a particle diameter of 15 nm or more and 29 nm or less and a second group of ITO particles having a particle diameter of 30 nm or more and 60 nm or less, wherein the mass ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group is 8% or more and 75% or less.

24. The ITO film according to claim 23, wherein the mass ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group is 25% or more and 75% or less.

25. The ITO film according to claim 23, wherein the mass ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group is 8% or more and 50% or less.

26. An ITO film according to any one of claims 23 to 25, wherein the mass ratio of the first ITO particle group to the total mass of the first ITO particle group and the second ITO particle group is 25% or more and 50% or less.

27. A laminate comprising the ITO film according to any one of claims 23 to 26.

28. The laminate according to claim 27, which is a solar cell or an EL device.

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